1. Field of the Invention
The present invention relates generally to the field of automotive fuels, and more particularly to various gasoline-ethanol blends commonly referred to under the broad heading of "gasohol." Gasohol typically comprises blends of up to approximately 10 vol.% ethanol in gasoline, and is considered one of the leading sources for supplementing or replacing petroleum fuels such as gasoline.
More specifically, the present invention relates to a process for the production of such gasoline-ethanol blends by dehydrating an aqueous ethanol, preferably the aqueous ethanolic product from a conventional fermentation process, comprising from about 4 to about 12 wt.% ethanol, preferably about 6 wt.% ethanol, so as to generate an effluent containing about 90 wt.% ethanol; extracting such effluent with a gasoline at a low, sub-ambient temperature, thereby enabling the water concentrations present in the gasohol produced in such process to be carefully controlled and the excess thereof separated from the ultimate gasohol blend and restored to the overall process for purposes of further extraction.
2. Description of the Prior Art
Dehydration of alcohols, particularly of ethanol, is a well-known art, and the methods generally used for such dehydration have either involved use of azeotropic distillation (see, e.g., U.S. Pat. Nos. 2,140,694; 2,173,692; and 2,358,193) or of non-distillation methods exemplified by the use of various adsorbents, such as shown by U.S. Pat. No. 2,137,605. Furthermore, it is also well known in the art that extraction is another method for the dehydration of alcohols or mixtures of alcohols. For example, U.S. Pat. No. 3,052,731 shows the use of hexane to separate, by extraction, water and a mixture of alcohols obtained as a result of partial oxidation. Moreover, in a more specific application of extraction, i.e., with hydrocarbons, U.S. Pat. No. 3,455,664 shows the use of gasoline extraction to achieve dehydration, but such use is essentially shown to be restricted within the context of isopropyl alcohol synthesis, through mixing of the gasoline with the isopropyl alcohol reaction product, and it involves a subsequent separation step conducted under considerable pressure, e.g., a pressure greater than 2,000 p.s.i.
It is also known to make gasoline and alcohol blends and utilize such blends in internal combustion engines of the Otto type, i.e., those which use spark plugs. For example, U.S. Pat. No. 1,699,355 discloses treating gasoline with alcohols to prevent "knocking" in internal combustion engines. However, the resultant gasohol product contains too much water for today's motor fuel standards since it has been saturated with water at temperatures in excess of those which might be encountered during the operation of the engine and thus might generate an undesired water phase upon occasional cooling. On the other hand, the prior art, including that which has been discussed above, has been generally of the opinion that the costs of energy consumption needed to produce gasohol by heretofore conventional means are too high, thereby making gasohol too costly an alternative to gasoline for use as fuel. In addition, control of the water content in gasohol blends, an element vital to the successful use of such blends as fuels for internal combustion engines, and removal of excess water from conventionally produced gasohol blends by known means, involve additional cost and separation problems, associated with increased capital investments and energy consumption.
The present invention, however, is quite adept at filling all these prior art voids in that it greatly reduces the amount of energy necessary to produce gasohol while concurrently providing means for achieving acceptable water levels in the gasohol produced. Because the distillation of ethanol from a 6 weight % fermentation feed to a 90 weight % effluent product ethanol requires relatively low energy consumption, much lower, for example, than the energy required for producing 95 weight % ethanol or anhydrous ethanol, this factor can be exploited to great advantage by producing gasohol directly from blending such 90 weight % effluent ethanol with a conventional gasoline or gasoline source. In this manner, the overall energy consumption involved in the production of gasohol is significantly reduced when compared to the energy consumed by known and/or previously used methods for producing gasohol.
Moreover, since it is also well known that gasohol blends must not have a water content so high as to cause the separation of an aqueous phase during storage, transportation, distribution, and use, the fact that the present invention solves this problem concurrently while providing means for greatly reducing the energy consumption required to produce gasohol makes the present process for producing gasohol quite attractive commercially.
Through deployment of appropriately situated heat exchangers in the overall process, moreover, energy consumption and costs related to the cooling process can also be sharply reduced.